The 'ticket' and 'my_ticket' arguments are both read and written within
the same asm block. Clang is stricter with the constraints than gcc4
was, so accepts the '=r' at face value and will happily overwrite
registers that "should" be preserved.
Mark these operands to not clobber other operands, so they get their own
registers.
This fixes a panic on bringing up the octe interfaces.
